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<head><meta charset="utf-8"><title>Effects of MIR otimizations on Miri UB detection · t-compiler/wg-mir-opt · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/189540-t-compiler/wg-mir-opt/index.html">t-compiler/wg-mir-opt</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/189540-t-compiler/wg-mir-opt/topic/Effects.20of.20MIR.20otimizations.20on.20Miri.20UB.20detection.html">Effects of MIR otimizations on Miri UB detection</a></h3>

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<a name="210662127"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/189540-t-compiler/wg-mir-opt/topic/Effects%20of%20MIR%20otimizations%20on%20Miri%20UB%20detection/near/210662127" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> RalfJ <a href="https://rust-lang.github.io/zulip_archive/stream/189540-t-compiler/wg-mir-opt/topic/Effects.20of.20MIR.20otimizations.20on.20Miri.20UB.20detection.html#210662127">(Sep 20 2020 at 11:22)</a>:</h4>
<p>Some recent MIR optimization changes affect Miri UB detection at mir-opt-level=2, meaning that either there is no more UB at higher opt-levels or the kind of UB changes. This is completely fine and Miri sets mir-opt-level=0 exactly for this reason, but I thought it might be interesting for you to look at these diffs in the Miri test suite and determine if this is an expected outcome of whatever changes recently landed:</p>
<ul>
<li><a href="https://github.com/rust-lang/miri/pull/1538">https://github.com/rust-lang/miri/pull/1538</a></li>
<li><a href="https://github.com/rust-lang/miri/pull/1552">https://github.com/rust-lang/miri/pull/1552</a></li>
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<a name="210662386"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/189540-t-compiler/wg-mir-opt/topic/Effects%20of%20MIR%20otimizations%20on%20Miri%20UB%20detection/near/210662386" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Jonas Schievink  [he/him] <a href="https://rust-lang.github.io/zulip_archive/stream/189540-t-compiler/wg-mir-opt/topic/Effects.20of.20MIR.20otimizations.20on.20Miri.20UB.20detection.html#210662386">(Sep 20 2020 at 11:28)</a>:</h4>
<p>The generator move getting elided would be caused by dest prop if you run at mir-opt-level=2 or 3</p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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